The prima facie evidence for the age of the Proterozoic Kingston Peak Formation cited by Prave (1999) is the δ13C value of carbonate in metalimestones in the middle and upper parts of the formation. Those data and the C-isotope composition of the overlying Noonday Dolomite were used by Prave (1999) for correlation with a chemostratigraphic record for Neoproterozoic rocks to determine ages of 700 and 600 Ma for the Death Valley rocks. Our data (Bergfeld et al., 1996; Souza, 1991) show that the C-isotopic compositions of the Sourdough Limestone Member, other carbonate rocks in the...